You can use the ExtUtils::Installed module which provides a standard way to find what modules are installed. You can even install pmtools which will help you find the perl modules installed.
It can be downloaded from the following URL:
http://language.perl.com/misc/pmtools-1.00.tar.gz.

You can download the perl module from the CPAN site http://www.cpan.org/ and install it using the following command
perl -MCPAN -e \'install perl::module\'
A detailed documentation is available at the URL:
http://search.cpan.org/~jhi/perl-5.8.0/lib/CPAN.pm
Hope this helps you solve your problem.